This chapter examines the compressive strength of ordinary Portland cement paste blended with natural pulverized coconut fibers. Pulverized coconut fibers were mixed with Portland cement paste at different concentrations, 0% to 10% by weight (wt%), in order to evaluate its effect on microstructural and mechanical properties. Scanning electron microscopy (SEM) was used to observe the microstructure variation of the samples. The samples were mounted onto a resin mold in order for easier handling. Thereafter, they were mounted on an aluminum stub and gold sputtered with a Hummer 6.2 system, at conditions of 15 mA AC for 30s, in order to obtain a thin film of Au of around 1 nm. Fourier Transform Infrared spectroscopy (FTIR) spectra were collected with a Shimadzu apparatus with wavenumbers ranging from 500 to 3500 cm-1. Typical cement paste samples fabricated after 28 days of curing in the mold were made. The neat cement sample, comprising cement paste with 0.0 wt% of steel slag, was itself a multiphase composite material with typical cement phases.